In conventional integrated circuit fabrication, circuit elements are formed by etching a pattern of gaps in a layer of metal such as aluminum. The gaps are then filled with a dielectric such as silicon dioxide. Copper is poised to take over as the main on-chip conductor for all types of integrated circuits due to its lower resistance as compared to conventional aluminum alloys. Unfortunately it is difficult to etch copper and therefore, damascene processes have developed for fabrication of copper-based integrated circuits. In damascene processes, dielectric layers are deposited to form an integrated stack and then etched to form gaps that are subsequently filled with copper.
HDP-CVD fluorine-doped silicon oxide, also known as fluorosilicate glass (FSG) is an attractive solution to replace conventional silicon dioxide as intermetal dielectrics for damascene structures. FSG can be deposited in a conventional HDP-CVD systems which have been widely used for undoped silicate glass (USG) and FSG dielectrics in Aluminum interconnects. FSG has a good process scheme in terms of reliability, stability and throughput. The electrical performance of integrated circuits can be significantly improved due to the lower dielectric constant of FSG (about 3.3-3.6 compared to about 4.1-4.3 for conventional silicon oxides). The lower dielectric constant reduces the capacitance between metal lines in the same layer and reduces cross talk across layers.
The dielectric layers that separate layers of copper in a damascene structure are often referred to as intermetal dielectric (IMD) layers. IMD layers typically include a barrier layer to prevent diffusion of copper into adjacent dielectric layers such as FSG. Some integrated stacks used in damascene processes also utilize a layer known as an etch stop or hardmask to provide for selective etching of the film. Silicon nitride (SixNy) is commonly used as a barrier layer or etch stop in damascene applications, for example when forming vias between layers containing metal lines. Unfortunately, silicon nitride has a relatively high dielectric constant k≈7.0 to 7.5 compared to 4.0-4.2 for silicon oxide or 3.3-3.6 for FSG, k. Consequently a dielectric layer containing silicon nitride will have an undesirably high fringe capacitance.
Generally, the thicker the layer of silicon nitride, compared to the FSG thickness, the larger the overall dielectric constant for the integrated stack. The effective dielectric constant of an integrated stack depends on the thickness and dielectric constant of each layer comprising the integrated stack. The dielectric constant of the overall film can be reduced either by reducing the thickness of the barrier layer or by using a barrier layer material with a lower dielectric constant. Present deposition processes can deposit suitable SixNy films as thin as a few hundred angstroms in thickness or more. Existing techniques generally cannot deposit thinner films while maintaining the desired uniformity and overall film quality. Silicon-carbon-hydrogen based low-k barrier layers have been developed such as BLOK(trademark) (Barrier Low K). BLOK(trademark) is a trademark of Applied Materials, Inc. of Santa Clara, Calif. Such low-k barrier layers are typically deposited by plasma enhanced chemical vapor deposition (PECVD) using trimethylsilane (TMS). BLOK deposited using TMS provides capping solutions suitable for numerous processes, however alternative applications are desirable to enhance process integration.
Therefore, a need exists in the art for an inexpensive method of depositing an integrated stack including a low dielectric constant barrier layer that can be readily integrated with dielectric layer deposition.
The disadvantages associated with the prior art are overcome by a method of depositing a film, such as a barrier layer, on a substrate using a gaseous mixture that includes a silicon containing gas, and a hydrocarbon gas. The method generally comprises providing the gaseous mixture to the chamber, generating a plasma from the gaseous mixture, and depositing a film onto the substrate using the plasma. In one embodiment, the thickness of the barrier layer is less than 500 xc3x85. In another embodiment, the barrier layer is less than 150 xc3x85. Suitable hydrocarbon gases include alkanes having the general formula CxH2x+2. Suitable alkanes include methane (CH4), ethane (C2H6), butane (C3H8), propane (C4H10), etc. Suitable silicon containing gases include silanes having the general formula SiyH2y+2. The gaseous mixture may optionally include a flow of argon (Ar) to promote gas dissociation. In one embodiment, the plasma is a high-density plasma. The gaseous mixture may have a carbon:silicon ratio of greater than 1:1, such as between about 3:1 and 8:1. The resulting film has a C:Si ratio ranging from about 55:45 to 65:35. Embodiments of the method of the present invention can deposit integrated stacks having an overall dielectric constant of about 4.0 or less. Such a stack may include a barrier layer having a dielectric constant of 3.0 or less. Integrated stacks and barrier layers deposited according to the present invention may be used in intermetal dielectric layers for dual damascene structures.
The method of the present invention may be embodied in a computer readable storage medium having a computer-readable program embodied therein for directing operation of a substrate processing system. Such a system may include a process chamber, a plasma generation system, and a gas delivery system configured to introduce gases into the process chamber. The computer-readable program includes instructions for operating the substrate processing system to form a film on a substrate disposed in the processing chamber in accordance with embodiments of the above method.
These and other embodiments of the present invention, as well as its advantages and features are described in more detail in conjunction with the text below and attached figures.